The present invention relates to a multiple axes planetary transmission wherein each axis includes a synchronizer operatively connected between an input clutch and a planetary gear set for speed shifting.
Vehicle transmissions for use in conventional automobiles are typically manual- or automatic-type transmissions. Manual transmissions include a clutch pedal and a gear shift lever which must be coordinated by a driver in order to select the desired speed. Automatic transmissions eliminate the need for a clutch pedal because all speed shifting is achieved automatically within the transmission. This is accomplished by means of a torque converter which provides a smooth coupling between the engine and the transmission, and hydraulically-actuated clutches which control shifting of planetary gear members.
Parasitic losses in the torque converter and power usage in the pressurization of hydraulic fluid for clutch shifting generally results in lower fuel efficiency for automatic transmission vehicles in comparison to manual transmission vehicles. The development of electronic control systems has improved the shifting schedule and shift feel of automatic transmissions, and has eased the implementation of fourth and fifth overdrive gears, thereby increasing fuel economy.
Recently, manual layshaft-type transmissions have been provided with automated shifting operation in the so-called dual input automated manual layshaft-type transmissions. Examples of these configurations are shown in U.S. Pat. Nos. 6,044,719 and 6,286,381.
The present invention provides a new automatic or manual planetary transmission arrangement which includes two or more axes within a transmission housing. Each axis includes an input friction energy absorbing clutch, a single planetary gear set, and a synchronizer-type coupling element.
More specifically, the invention provides a transmission arrangement for a vehicle, including a transmission housing with at least two transmission axes extending within the transmission housing. Each of the axes includes an input transfer gear engaged with an input clutch, wherein the input clutch is connected to at least one member of a planetary gear set. Each axis also includes an output transfer gear driven by a member of the planetary gear set, and a synchronizer-type coupling element operatively connected between the input clutch and the planetary gear set for selectively engaging and disengaging members of the planetary gear set with respect to the input clutch and transmission housing.
Preferably, one of the transmission axes includes a reverse speed synchronizer operatively connected between the respective planetary gear sets and output transfer gear for selectively reversing rotation of the respective output transfer gear.
The transmission arrangement of the invention may be used for a manual or automatic transmission. The transmission arrangement may be a four-speed transmission having two transmission axes, a six-speed transmission having three transmission axes, or an eight-speed transmission having four transmission axes, and so on.
In one embodiment, a six-speed transmission has three transmission axes. A first axis has components configured to provide second and fifth forward speed ratios. A second axis has components configured to provide reverse, first and fourth forward speed ratios. A third axis has components configured to provide third and sixth forward speed ratios.
Each synchronizer-type coupling element is configured to selectively connect one of the planetary gear members with the transmission housing or with another one of the planetary gear members, wherein said another one of the planetary gear members is connected to an output side of the input clutch.
The synchronizer-type coupling elements are selectively prepositioned for speed selection while the respective shaft is unloaded before the respective-input clutch is engaged to shift a load from a loaded axis to the unloaded axis. The input clutch on the loaded axis is disengaged as the input clutch on the unloaded axis is engaged to achieve clutch-to-clutch shifting between axes.
The input clutch on one of the axes may be identified as an input starting clutch which launches the vehicle from a stopped position, thereby eliminating the torque converter. This transmission may also be used with a torque converter.
By using synchronizers rather than clutches, cost and control complexity may, be reduced. In this configuration, the synchronizers and clutches on different axes would be common parts which would reduce design and manufacturing costs. The synchronizers are also easier to move than the clutch because a clutch requires significant hydraulics and multiple components for, shifting. The synchronizers are xe2x80x9con-offxe2x80x9d clutches which are controlled electronically, manually or hydraulically. One-way clutches are not required to smooth the gear shifting because of the clutch-to-clutch shifting, but may be used if desired.
This transmission arrangement also provides significant flexibility. For example, whereas a dual clutch automated transmission cannot skip speeds, the present design can skip speeds (i.e., first-to-third, second-to-fourth, or third-to-fifth). Also, the direct-drive ratio may be provided in different gears, depending upon the configuration of the transmission.
The axes could be arranged such that the transfer gear associated with the second or third axis would engage the transfer gear of the first axis.